Thermally responsive device



April 30, 1940. R. R. PITTMAN r A1. ,2,198,840

THERMALLIRESPONSIVE DEVICE Filed Ju1yJ1'7/1939 A@ @P y.;

Patented Apr. 30, 1940 PATENT ori-ICE THERMALLY RESPONSIVE DEVICE RalphB.. Pittman and Carroll H. Walsh, Pine Blull, Ark.

Application July 17, 1939, Serial No. 284,928

4 Claims.

This invention relates generally to electrical devices actuated inresponse to a movement of a thermally responsive element. Moreparticularly, it relates to a thermally responsive ele- '5 ment for usein such devices, and an indicating device incorporating the element.

Among the objects of the present invention may be noted (a) theprovision of a thermally responsive element in which the controllingmovement may be the same in distance as elements heretofore used but inwhich the time for accomplishing the movement may be much greater; (b)the provision of indicating means controlled by the element, such thatthe organization is peculiarly adapted to indicate certain predeterminedpoints of the temperature characteristic of electric apparatus,particularly insulated self cooled transformers, which are in a circuitwith the element; (c) the provision of a so thermally responsive elementincluding a bimetallic strip which bends when heated and on which ismounted, for movement in response to the bending of the bimetallicstrip, a heater-strip of relatively higher resistance material which udoes not bend when heated, the bimetallic and heater strips beingelectrically in series circuit relation; and (d) an indicating device,including the thermally responsive element, embodying a novelarrangement for shunt-clr'cuiting the 3 element in response topredetermined movement of the indicator.

The present inventionis` a continuation in part of our pendingapplication Serial No. 212,- 613, nled June 8, 1938.

With the above and other objects in view which will appear as thedescription proceeds, our invention resides in the novel combination,construction and arrangement of the parts, and the scope of theinvention will be pointed out in the appended claims.

In the drawing, in which similar reference characters indicatecorresponding parts:

Fig. 1 is a side elevational view of the device, illustrated with oneside of the housing removed 45 to show the members within.

' Fig. 2 is a section taken along the line II-II of Fig. 1.

Fig. 3 is an end view of the device, shown with the housing closureremoved.

50 Fig. 4 is a fragmentary view of the terminal arrangement.

Referring new to the drawing, a hollow metal housing I0, having aforwardly extending holthe screws 48 and 49. An indicator 39 ispivotally mounted at one end thereof on the housing l0 bymeans of theshaft 44 extending laterally therethrough, the indicator bearing 45being journalled for rotative movement about the latter. A centralslotted opening 50 extends longitudinally along the closure H, and theindicator-semaphore 40 is arranged to move through the opening 50 intoand out of the housing Iii.4

A pair of spaced insulated conducting termil0 nais I2 and I3 extenddownwardly through the top of the .housing I0 'in spaced ,relationshiptherewith, and in threaded engagement with the internal downwardlyextending spaced metal supports and 2|. .The latter are respectively ldl clamped against the internal insulating block Il by means of the nutsI4 and l5, and an external insulating block I6 is interposed between thelatter andthe housing l0.

f The thermally responsive element, indicated in 20 its entirety by thenumeral 52 includes a pair of spaced .horizontally extending bimetallicstrips 22 and 34, which are rigidly secured to the sup'- ports 2| and 20respectively intermediate of the ends thereof by the screws 24 and 35respec- 25 tively. A pair of non-bimetallic heater-strips 23 and 33 arerigidly secured to the free ends of the bimetallic strips 22 and 34 bymeans of the rivets 25, and. spaced therefrom by the metal spacingblocks 5l, the heater-strips 23 and 33 30 tallic strips 22 and 34, andthence downwardly in spaced parallel relation to a point near the bottomof the housing I0 andy remote from the bimetallic strips 22 and 34.

From the above description, it may be seen that the thermally.responsive element includes a series circuit arrangement of a bimetallicstrip n and al non-bimetallic strip.1 so arranged that a small movementof the former due to rise in temperature thereof causes a relativelylarger movement of the free end of the latter. The nonbimetallic stripis of relatively high resistance metal, so that the heat therefrom willbe slowly conducted to the bimetallic strip, thus slowly heating thebimetallic strip, and thereby delaying its bending movement due toheating. We have found Monel metal a suitable material for lthenon-bimetallic heater-strip. The rate of transfer of heat from theheater strips to the bimetallic strips may also be varied by a change inthe distance which separates the parallel portions oi.' these strips, asthe heater strips, being 55 located under the bimetallic strips, radiatea portion of theheat of the former to the latter.

A latch member 30 is rigidly secured to the indicator 39 by means of therivets 31 and 42,

being electrically insulated from the indicator 33 by the sleeves ofinsulating material 38. (Fig. 2.) The latch member 30 extends toward thelower juncture of the heater-strips 23 and 33, and is provided with apair of detents 3| and 32, the former having a. smaller radius ofrotation about the shaft 44 than the latter. When the semaphore 40 is inthe concealed position indicated by the solid lines of Fig. l, thedete'it 3| is engaged with the portion joining the lower ends of theheater-strips. In response to a movement of the lower end of theheater-strips in a direction away from the shaft 44, the detent 3| isdisengaged, and the indicator 39 rotated about the shaft 44 under theinfluence of the spring 43, which has one end fastened to the indicator39 and the other end engaged with the inner vertical surface of thehousing l0. The

indicator 39 is rotated in a clockwise directionuntil the second detent32 engages the portion joining the lower end of the heater-strips, andremains in this position until a further outward movement of theheater-strips takes place. In response to such movement, the detent 32is disengaged and the indicator then assumes a po-` sition substantiallyendwise of the housing I0.

The degree of engagement of the detents 3| and 32 `may be varied bymeans of the externally extending adjusting screws i8 and I9, which arearranged to laterally shift the thermally responsive element assembly ina direction to either increase or decrease the extent of engagement ofthe detents with the thermally responsive element. This arrangement isof assistance in adjting the device following assembly.

To prevent damage to the thermally responsive element under heavycurrents due to faults in the connected circuit, a novel shuntingarrangement is embodied in the device. The conducting supports' 20 and2| are provided with the downwardly extending portions 41 and 26respectively, and the contacts 46 and 21 provided at the respectivelower ends "thereof, circuiting metal bar 28 is rigidly secured to thelower ends of the heater-strips 23 and 33, by means of the rivets 29 and36, and the contacts 46 and 21 positioned in the path of movement of thebar 28. Upon the occurrence of a movement of the thermally responsiveelement which releases the second detent 32, the bar 28 is engaged bythe arcuate portion 53 of the latchmember 30, and thus driven and heldtightly against the contacts 21 and 46, shunt-circuiting the thermallyresponsive element and preventing the passage of excessive and damagingamounts of current therethrough.

The normal path of current through the device from the terminal I3includes serially the support 2|, the bimetallic member 22; thenonbimetallic heater-strip 23, the non-bimetallic lheater-strip 33, thebimetallic member 34, the

support 20, and the terminal I2.

A practical application of the device is to the indication oftransformer loading. In such an application, it is desirable that theindications follow the temperature-time curve of the copper in theconnected transformer. Because of the mass of the winding in atransformer, and of its intimate association with the cooling medium,considerable time is required for a transformer carrying rated load toreach its maximum rtem- A shunt-I perature. In order to conform to theheating characteristic of such a structure, and at the same time obtainsumcient movement for definite latch control, we arrange the indicatorso that the bimetallic element is heated both from the current passingtherethrough and from the heat conducted and radiated from theheater-strip to the bimetallic strip. 'I'he accumulation of the heatnecessary to cause sufficient deflection of the bimetallic strip torelease the indicator may be delayed for a much longer time with thearrangement above described `than if only a bimetallic strip, or a usualarrangement of blmetallic strip and associated heater, was em.-

ployed. This time may be varied to a certain extent through the use ofcombinations of strips which differ in electrical and physicalcharacteristics, and by varying the distance between the heater and thebimetallic strips.

In the preferred form, the indicator is calibrated to indicate one ofthree conditions of a connected transformer. If the indicator has notmoved from its concealed position, the transformer is underloaded, and asmaller unit may be safely and economically substituted. If theindicator has moved to a position approximately 45 degrees with theplane of the bottom of the housing, the transformer is operating in theeconomical range at substantially full load. If the indicator has movedto a position substantially endwise of the housing, the transformer hasbeen subjected to overheating, and should be replaced with a larger unitbefore it is destroyed. While the three indications above recited arebelieved to show the essential conditions for practical considerationsit will be apparent that additional detents may be readily added tothelatch member 30 to provide additional indications.

Specific language has been used in describing the embodiment of theinvention herein presented, but it will be understood that this has beendone to facilitate an understanding of the construction and operation,and that various changes may be made in the specific'- constructionwithout departing from the principles of the invention.

We claim. as Vour invention:

1. In an electric thermal indicating device, for an electric circuit, amovable indicator having a plurality of indicating positions, includinga final position, a latch member having detents, said latch member beingmovable with said indicator, and a thermally responsive element inseries relation with said circuit and having a portion movable withrespect to said latch member and normally engaging one of saiddetents torestrain movement of said indicator, means responsive to a predeterminedmovement of the movable portion of said thermally responsive element formoving said indicator to the final position, and means responsive to themovement of said indicator to the final position for shuntcircuitingsaid thermally responsive element, said last-named means including a camportion of said latch member, a relatively low resistance member mountedon said movable portion of said thermally responsive element andpositioned in the path of movement of said portion, and a pair ofspacednormally insulated conducting contacts electrically connectedrespectively to the respective ends of said thermallyresponsive elementand constructed and arranged to be bridged by said low resistance memberin response to a predetermined movement thereof.

2. In an electric thermal indicating device for an electric circuit, amovable indicator having a plurality of indicating positions including aiinal Iposition, a latch member having detents, said latch member beingmovable with said indicator, a thermally responsive element electricallyconnected in series relation with said circuit and having a movableportion normally engaging one of said detents, means responsive to apredetermined movement oi said movableportion for actuating saidindicator to the iinal position, and

means for shunt-circuiting said thermally responsive element followingsaid movement, said last-named means including normally insulatedconducting contacts electrically connected to the respective ends ofsaid thermally responsive element, a conducting member movable into andout of engagement with said contacts, and a cam portion of said latchmember arranged to engage and urge said conducting member intoengagement with said contacts.

3. In an electric thermal indicating device for an electric circuit, athermally responsive element having a movable portion, means forelectrically connecting said element in said circuit,

an indicator movable to an indicating position,

a Alatch member rigidly secured to said indicator and normally engagingthe movable portion of said thermally responsive element for restrainingthe movement o! said indicator, a relatively low resistance membermounted on the movable portion of said thermally responsive element, apair of spaced normally insulated contacts electrically connected to therespective ends of said thermally responsive element, means responsiveto a predetermined movement of said thermally responsive element foractuating said indicator to the indicating position, and means forurging said low resistance member into bridging engagement with saidcontacts `following said movement, said last-named means including a camportion oi said latch member arranged to engage said low resistancemember when said indicator has moved to the indicating position.

4. In an electric thermal indicating device for van electric circuit, athermally responsive element having a movable portion, means forelectrically connecting said element in said circuit; an indicatorswingably movable to an indicating position, resilient means urging saidindicator to the indicating position, a latch member rigidly securedto-said indicator and normally engaging the movable portion of saidthermally responsive element for normally restraining the movement ofsaid indicator and for unlatching said indicator in response to apredetermine movement of the movable portion of said thermallyresponsive element, and'means responsive to the unlatching of saidindicator for shunting said ther-

